1. Field of the Invention
The present invention relates to a method of forming a pattern. More specifically, the present invention relates to a method of forming a pattern that is suitable for use in an ultramicrolithography process applicable to a process for manufacturing a super-LSI or a high-capacity microchip, a process for fabricating a nanoimprint mold, a process for producing a high-density information recording medium, etc. and other photofabrication processes. Particularly, the present invention relates to a method of forming a pattern that is suitable for exposure using a liquid-immersion projection exposure apparatus in which a far-ultraviolet light of wavelength 300 nm or shorter is employed as a light source.
In the present invention, the terms “actinic rays” and “radiation” mean, for example, a mercury lamp bright line spectrum, far ultraviolet rays represented by an excimer laser, extreme ultraviolet rays, X-rays, electron beams and the like. In the present invention, the term “light” means actinic rays or radiation.
The expression “exposure” used herein, unless otherwise noted, means not only light irradiation using a mercury lamp, far ultraviolet, X-rays, EUV light, etc. but also lithography using particle beams, such as an electron beam and an ion beam.
2. Description of the Related Art
Since the emergence of the resist for a KrF excimer laser (248 nm), it has been of common practice to employ a pattern forming method in which chemical amplification is utilized in order to compensate for any sensitivity decrease caused by light absorption. In this method, a photosensitive composition containing a resin that decreases its solubility in an alkali developer when acted on by an acid, and an acid generator that generates ac acid upon an exposure of light is typically employed (see, for example, patent references 1 to 5 and non-patent reference 1).
In a positive chemical amplification method, first, a film is formed by using a photosensitive composition. Subsequently, the film is exposed to light. Thus, at least a part of a photoacid generator contained in exposed areas is decomposed by light irradiation to thereby generate an acid. Then, the generated acid exerts a catalytic action so that the alkali-insoluble group contained in the photosensitive composition is converted to an alkali-soluble group. Thereafter, development is carried out using an alkali solution. Thus, the exposed areas are removed to obtain a desired pattern.
As the alkali developer, an alkali aqueous solution with strong basicity is usually employed. In the process of manufacturing semiconductors, etc., 2.38 mass % TMAH (tetramethylammonium hydroxide) solution is used as a standard alkali developer (see, for example, patent references 1 to 5 and non-patent reference 1). The concentration of 2.38 mass % was fixed for optimizing a dissolution velocity of g-ray or i-ray resist. However, the use of 2.38 mass % TMAH solution has also become a de facto standard in other resists now being investigated.